1. Field of the Invention
This invention relates to a novel catalyst comprising a zeolite containing one or more Group VIII noble metals in which the noble metal is highly dispersed throughout the zeolite. This catalyst is capable of terminally cracking various organic compounds and exhibits a sustained maintenance under reforming conditions and improved selectivity for aromatization products.
2. Discussion of the Relevant References
Several materials have been employed as hydrocarbon conversion catalysts in such processes as reforming, catalytic dewaxing, alkylation, oxidation and hydrocracking. Examples of catalysts useful for this purpose include those materials comprising a catalytically active metal such as a Group VIII noble metal and optionally rhenium supported on or impregnated into a carrier.
Among the hydrocarbon conversion processes, catalytic reforming in the presence of hydrogen is one of the most important. Catalytic reforming is a refinery process designed to increase the octane number of naphtha. Typically in this process, the naphtha is passed over a suitable catalyst under reforming conditions for example, elevated temperatures and pressures, well known in the industry in the presence of hydrogen gas and a h.sub.2 /hydrocarbon mole ratio of 2 to 20. This process involves several different types of reactions, including isomerization, dehydrocyclization of paraffins to produce naphthenes and aromatics, dehydrogenation of cyclohexanes and other naphthenes and alkanes, isomerization/dehydrogenation of cyclopentanes, isomerization of normal paraffins to isoparaffins, and hydrocracking. Paraffin isomerization occurs relatively easily, but contributes only a limited improvement in octane number. The reforming reactions most important for the production of high octane components are those which produce aromatics.
The ideal reaction scheme minimizes the hydrocracking of long chain paraffins to gaseous hydrocarbons such as methane and ethane to improve the yield and selectivity to more valuable products of the other reforming reactions, particularly dehydrocyclization. Examples of known catalysts useful for reforming include platinum and optionally rhenium or iridium on an alumina support, platinum on type X and Y zeolites, provided the reactants and products are sufficiently small to flow through the pores of the zeolites, platinum on the intermediate pore size zeolites as described in U.S. Pat. No. 4,347,394 and platinum on cation exchanged type L zeolites.
While zeolite L catalysts, usually in their hydrogen form, have been employed as catalytic dewaxing catalysts and in other applications, they are particularly useful in reforming because they decrease the amount of hydroacracking which occurs during reforming. For example, U.S. Pat. No. 4,104,320 to Bernard et al. discloses that the use of zeolite L as a support increases the selectivity of the reaction for producing aromatic products. This improvement, however, has been made at the expense of catalyst life. This catalyst may be regenerated by subjection to a hydrogen treatment, oxidation, oxychlorination, calcining, water treatment, and reduction with hydrogen as disclosed in French Patent Publication No. 2,360,540 filed Sept. 9, 1981 to Bernard et al., or by hydrogen regeneration as disclosed in French Appl. No. 8,000,114 to Bernard. These regeneration techniques, however, have not been applied to freshly prepared catalysts which are defined for purposes herein as catalysts which have not been contacted with a hydrocarbon feed.
U.K. Appln. No. 82-14147 filed May 14, 1982 to Wortel entitled "Improved Zeolite L" teaches that a highly crystalline zeolite L material having a cylindrical morphology has an improved catalyst life for dehydrocyclization reactions over a conventionally prepared zeolite L disclosed in U.S. Pat. No. 3,216,789. U.S. pat. appln. Ser. No. 426,211 filed Sept. 28, 1982 to A. Cohen entitled "Improved Zeolite L Catalyst for Reforming" discloses treating a zeolite L material with an alkali solution of pH of at least 11 prior to calcining the formed catalyst so as to improve the dehydrocyclizing activity of the catalyst. Finally, Belg. Pat. Nos. 895,778 and 895,779 disclose use of a barium-exchanged zeolite L catalyst for high yields in reforming, dehydrocyclization, dealkylation and dehydroisomerization.